Super critical fluid chromatography allows to separate a component, i.e. an extractant from another component, i.e. a matrix, by making use of a super critical fluid as the extracting solvent. By means of SFC and HPLC, various substances can be chemically analyzed, identified and quantified. Making use of carbon dioxide as a super critical fluid in SFC applications, the extraction of the substances has to be conducted under super critical conditions. Regarding carbon dioxide as the super critical fluid of choice, the extraction has to be conducted above the critical temperature of 31° C. and above a critical pressure of 74 bar.
For keeping CO2 or a CO2-mixture in a liquid state inside a chromatography column, the entire chromatography system has to be kept on a predefined pressure level. For this purpose, downstream of the chromatography column and downstream of a respective detector, a back-pressure regulator is typically provided, to keep the pressure inside the chromatography system on a predefined level.
In practical applications, SFC-technology comes along with the disadvantage, that a mobile phase of chromatographically separated substances cannot be easily collected in opened vessels. As soon as a mixture of liquid CO2 and an additional solvent is exposed to atmospheric pressure, CO2 abruptly expands and forms an aerosol with the additional solvent. A loss-less collection of the solvent requires sufficient gas-liquid separation of the aerosol.
Gas-liquid mixtures can be generally separated into a gaseous and into a liquid component by making use of inertia separators which operate according to the cyclone principle. There, an aerosol is tangentially inserted into a cone-shaped vessel. The aerosol propagates on a circular path so that its liquid particles drift radially outwardly until they impinge on the sidewall of said vessel. Due to their reduced mass, gaseous components experience less inertia force and may leave the cone-shaped vessel by means of a central immersion tube.
In SFC, the composition of the aerosol may strongly vary. The mixture of CO2 and an additional solvent, such like methanol may vary from 10% to 60% methanol fraction. As a consequence, the constitution of the aerosol and its volume flow may vary accordingly thus leading to sub-optimal rates of separation of gaseous and liquid fractions of the aerosol in a cyclone-type separator.
Other gas-liquid separation systems for instance make use of impact separation, wherein the volume flow of the aerosol is directed onto a deflector plate, which may be even provided by a test tube.
In general, impact separators and inertia separators require a comparatively large volume into which the aerosol should expand. Such comparatively large vessels are not optimal in terms of self-cleaning effects and may therefore provide cross contamination of aerosols and substances being sequentially processed by such separators.
In principle, the size and the surface of impact separators can be minimized when operating at a raised pressure level. For instance, a test tube serving as a deflector plate can be provided in a pressurized environment. The aerosol may then escape from a bent outlet and may impinge on the sidewall of the test tube at a predefined angle. With such an impact separator it is indeed possible to collect smaller amounts of a substance at a much lower degree of cross contamination. But impact separators operating at a raised pressure level do not allow to realize a large scaled automated fractionation.
Hence, operating expenses and costs are comparatively high since only a limited amount of test tubes can be automatically processed in the pressurized area. Moreover, the rate of separation is not as good as with impact separators operating at atmospheric pressure.
It is therefore an object of the present invention to provide an improved gas-liquid separator featuring an improved rate of separation of gaseous and liquid components of an aerosol. The gas-liquid separator should further provide a high rate of separation even when the constitution and composition of the aerosol changes. Moreover, the gas-liquid separator should provide efficient separation of CO2 and a solvent, like methanol, especially for SFC-applications. It is a further object of the invention to provide gas-liquid separation, which allows to realize a large-scaled automated fractionation and fraction collection for SFC, preferably at atmospheric pressure.